Core Concepts and Principles
The thinking before the toolkit
This domain tests whether you know principles and can tell them apart from tools. The recurring principles are: value is defined by the customer; work is a process and processes vary; variation has causes that can be found; most delay comes from the system, not the individual; improvement needs a standard to improve from; and people closest to the work know most about it.
Frameworks to know cold
- PDCA / PDSA - Plan, Do, Check/Study, Act. It is a loop, not a waterfall. "Act" means standardise or adjust the plan, then loop again.
- DMAIC - Define, Measure, Analyse, Improve, Control. Use for problems with unknown cause and existing process; it is data-led and ends with control, not celebration.
- Lean - removes waste (waiting, overproduction, inventory, motion, transport, over-processing, defects, unused talent) and levels flow.
- Six Sigma - reduces variation; a sigma level expresses defects per million opportunities.
- Theory of Constraints - find the bottleneck, exploit it, subordinate everything to it, elevate it, then repeat. Improving a non-bottleneck does not raise throughput.
- Kaizen - small, frequent, low-cost changes made by the team; contrast with kaikaku (radical redesign).
Traps
Assuming a tool equals a principle (deploying a fishbone diagram is not "systems thinking"); treating Lean as headcount reduction; treating PDCA as a one-pass project; and confusing the bottleneck with the busiest resource.
Worked example
A call centre adds staff in the department with the highest utilisation, but cycle time does not improve. Under the Theory of Constraints the correct question is where does work queue? - the upstream approval step with a three-day backlog. Adding capacity anywhere else only builds inventory.